The quality of plastic films used for horizontal silos is important to limit losses in the upper silage layer. The aim of this work was to study the effectiveness of different plastic films in reducing the top losses in maize silage. The following treatments were evaluated: (i) coextruded polyethylene/polyamide oxygen barrier film (OB), (ii) polyethylene film (PE), (iii) polyvinyl chloride film (PVC), and (iv) coextruded PE/polyvinyl alcohol film (PVOH). These treatments differed according to oxygen permeability with values of 75, 722, 982 and 289 cm3 m−2 per 24 hour respectively. OB and PVOH films had better temperature and fermentation profiles than the more permeable films. The OB film was effective in reducing the dry-matter (DM) losses during storage (82 g kg−1), and the PVOH film had an intermediate value of DM loss (101 g kg−1). PE and PVC films had higher losses (138 and 145 g kg−1 respectively). Oxygen permeability of the films promoted a positive correlation with DM losses (P < 0·05; r2 = 0·945). The results indicate that O2 permeability through the plastic film is a crucial factor for maintaining silage quality in the upper layer of the silo when it is perfectly sealed.